Remote detonation of explosive charges

Abstract

Explosive charges are detonated by remote control in environments having high levels of extraneous electric and electromagnetic energy by providing a separate control unit for each explosive charge. The control unit accepts coded commands radio transmitted from a command unit and, if those commands meet with pre-set criteria, the control unit detonates the charge. Each control unit is connected to its respective explosive charge by electrical or optical conductors providing sufficient separation as to allow the control unit to survive detonation of the charge without damage.

I claim: 
     
       1. A device for remotely detonating explosive charges in environments having high levels of extraneous electricity including stray ground currents, electromagnetic fields and radio frequency energy, comprising: a command unit adapted to repetitively transmit a sequence of coded commands by radio;   a plurality of explosive charges, each of said charges having an electrically activated detonator;   a plurality of control units, one for each of said charges, each of said control units physically connected to one of said charges by signal transmitting means, said transmitting means having length sufficient to allow each said control unit to survive the detonation of its associated explosive charge, each control unit having decoding, logic and transmission means adapted to receive and decode distinctive radio commands from said command unit, to communicate back to said command unit distinctive coded signals confirming receipt of commands from said command unit, and to send a signal through said transmitting means in response to a particular one such command, said signal causing detonation of said charge; and   current flow limiting means adapted to prevent said stray ground currents, electromagnetic fields, radio frequency energy and other extraneous electricity from inducing a current through said electrically activated detonator.   
     
     
       2. The device of claim 1 wherein each said control unit includes means adapted to recognize and discriminate among coded commands from said command unit and, in response to said commands, to cause the status of said control unit to change among inactive, alert, and armed states. 
     
     
       3. The device of claim 2 wherein said command unit is adapted to transmit coded commands comprising separate messages directed to each of said control units; said messages causing selected ones of said control units to change status from an inactive to an alert status and from an alert status to an armed status. 
     
     
       4. The device of claim 3 wherein said logic means of each said control unit are arranged to cause the control unit to revert to an alert status from an armed status if a predetermined time interval passes without the receipt of a new arm command from said command unit. 
     
     
       5. The device of claim 2 wherein said coded signals indicate the status of said control unit as well as confirm receipt of commands from said command unit. 
     
     
       6. The device of claim 3 including a translator unit adapted to relay said coded commands from the command unit to said control units, said translator unit including receiver means to pick up signals from said command unit and re-broadcast said signals to the control units. 
     
     
       7. The device of claim 6 wherein said translator unit also includes means to receive signals broadcast by said control units and to transmit said signals back to said command unit. 
     
     
       8. The device of claim 1 wherein said current flow limiting means includes electromagnetic shielding means surrounding said charge and said detonator. 
     
     
       9. The device of claim 1 wherein said electrically activated detonator is an electric blasting cap and wherein said current flow limiting means includes switch means arranged to connect and ground the two leg wires of said cap when said switch is in a deactivated position. 
     
     
       10. The device of claim 9 wherein said explosive charge, blasting cap and switch means are all arranged within a housing, said housing adapted to shield said blasting cap from electromagnetic radiation. 
     
     
       11. A method for remotely detonating explosive charges in environments having such high levels of extraneous electricity that safety considerations ordinarily require that electric blasting not be attempted comprising: providing a plurality of explosive charges, each of said charges having an electrically activated detonator;   preventing electrical currents induced by stray ground currents, electromagnetic fields, radio frequency energy and other sources of said extraneous electricity from flowing through said detonator;   coupling the detonator of each said charge to a control unit for said charge, said control unit adapted to receive distinctive coded commands from a command unit, to decode said commands, to communicate back to said command unit a distinctive confirmation that said commands have been received, and to respond to said commands; and   causing a surge of current to flow from each said control unit to its coupled detonator upon receipt and confirmation of a coded fire command transmitted to said control unit from said command unit.   
     
     
       12. The method of claim 11 wherein electrical currents are prevented from flowing through said detonator by surrounding said charge and the coupling between the charge and its control unit with an electromagnetic shielding. 
     
     
       13. The method of claim 11 wherein said detonator includes a bridge having leg wires and wherein electrical currents induced by said extraneous electricity are prevented from flowing through said bridge by connecting said leg wires together and to ground. 
     
     
       14. The method of claim 11 wherein each said coded command includes a preamble and a designation code sequence, said designation code sequence being unique to each control unit. 
     
     
       15. The method of claim 14 wherein said designation code sequence is a prime number. 
     
     
       16. The method of claim 14 wherein a first said coded command designates a control unit to be placed on an alert status and wherein said control unit transmits a message back to said command unit affirming the change in status of the control unit. 
     
     
       17. The method of claim 16 wherein a second said coded command designates a control unit which is on an alert status to go to an armed status in which state it can accept and act upon a third said coded command causing said control unit to detonate its coupled charge. 
     
     
       18. The method of claim 17 wherein said control unit reverts from the armed status back to an alert status in the event that a repeat of said second coded command is not received within a predetermined time interval. 
     
     
       19. The method of claim 17 in which said control unit repeatedly transmits a message back to said command unit affirming its change from an alert to an armed status.